1. Technical Field
The present disclosure relates to display devices and, more particularly, to display driving circuits, display devices, display systems and methods of driving display devices for a multi-display system.
2. Discussion of Related Art
A display device comprising a dual display format includes a main display panel and a sub-display panel. The sub-display panel displays a relatively small amount of information compared to the main display panel.
In the case of a folder type mobile phone, the main display panel, which is located inside of a folder cover, functions to display a phone number while dialing or an elapsed time of a phone call, etc. The sub display panel, which can be located in the outer side of the folder cover, functions to indicate information including signal reception strength during a stand-by mode, a clock, remaining battery power, etc.
A dual display structure offers improved functionality and convenience. However, problems may occur in an interface between a central processing unit (CPU) and a driving circuit for driving each of the display panels.
FIG. 1 is a block diagram illustrating a conventional dual display system.
Referring to FIG. 1, the conventional dual display system includes a first display panel 101, a first display driving circuit 102 for driving the first display panel 101, a second display panel 103, a second display driving circuit 104 for driving the second display panel 103 and a host 105.
As shown in FIG. 1, the first display driving circuit 102 is coupled to the host 105 via a first interface link represented by signal line 106, and the second display driving circuit 104 is coupled to the host 105 via a second interface link represented by signal line 107.
The host 105 provides video signals and control signals to the display driving circuits 102 and 104, and may be a type of processor. For example, the functions of the host may be performed by a base-band processor of a mobile phone. Alternatively, the functions of the host may be performed by another application processor.
In a system having a plurality of display driving circuits, the processor and the display driving circuits, which may be implemented as an integrated circuit (IC), and are connected to each other via a plurality of wires on a printed circuit board (PCB). As the number of the display driving circuits is increased, the wiring complexity between the processor and the display driving circuits is increased and electromagnetic interference (EMI) characteristics may be deteriorated.
Recently introduced mobile phones may include a display for displaying high-resolution video, or real-time images received from a built-in camera. Accordingly, data throughputs that the processor has to process have been increased, causing more severe EMI problems.
Compared to conventional parallel data transfer between the processor and the display driver IC, differential serial data transfer provides a high data transfer rate, low EMI and reduced wiring complexity. For example, display driver IC chips may incorporate Qualcomm's mobile digital display interface (MDDI) standard. According to the MDDI standard, data can be transferred between the processor, for example, the base-band processor of the mobile phone, and the display driver IC using a serial differential data transfer method.
The MDDI standard addresses at least four types of interfaces found in the communications and computer industries. These are labeled simply as type 1, type 2, type 3, and type 4. In the case of type 1, data may be transferred with a maximum data transferring rate of 400 megabits per second, and in the case of type 4, data may be transferred at a maximum data transferring rate of 3.2 gigabits per second. The connection wires between the baseband processor and the display driver IC may be reduced by applying the MDDI standard. For example, the number of wires connected between the baseband modem chip and the display driver IC may be reduced to about a tenth of the conventional 30˜40 wires.
Pixel data and control signals may be transferred through an MDDI interface or an 80-mode interface; however, the MDDI interface and the 80-mode interface may not transfer a video synchronization signal, or may have difficulty in transferring the video synchronization signal. When the interface is a unilateral interface, there may be a tearing effect that degrades the video image displayed on the sub-display panel when the synchronization signal of the sub-display panel is not sent to the main display panel. Generally, it is required that the synchronization signal of the sub-display panel is sent to the main display panel to prevent the tearing effect.
The conventional multi-display device may include a first display driver IC, which supports the MDDI interface, and a second display driver IC, which supports the parallel data transfer interface. For example, the display driver IC for driving the main display panel supports the MDDI interface, whereas the display driver IC for driving the sub-display panel supports the conventional parallel data transfer interface. Thus, in the conventional dual display system, the complexity of the wiring and the EMI characteristics may not be effectively improved when the first display driver IC adopts the serial differential interface.